package net;

import java.io.IOException;
import java.io.InputStream;
import java.io.RandomAccessFile;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;

/**
 * @projectName: java-sample
 * @description:
 * @author: Adam
 * @create: 2020-01-05 16:46
 **/

public class DownUtil {

    //定义下载资源的路径
    private String path;

    //定义所下载文件的保存位置
    private String targetFile;

    //定义需要使用多少个线程下载资源
    private int threadNum;

    //定义下载的线程对象
    private DownThread[] threads;

    //定义下载文件的总大小
    private int fileSize;

    public DownUtil(String path,String targetFile,int threadNum){
        this.path = path;
        this.threadNum = threadNum;
        //初始化threads数组
        threads = new DownThread[threadNum];
        this.targetFile = targetFile;
    }

    public void download() throws Exception{
        URL url = new URL(path);
        HttpURLConnection conn = (HttpURLConnection) url.openConnection();
        conn.setConnectTimeout(5*1000);
        conn.setRequestMethod("GET");
        conn.setRequestProperty("Accept","image/gif,image/jpeg,image/pjpeg,image/pjpeg," +
                "application/x-shockwave-flash,application/xaml+xml"
               +"application/vnd.ms-xpsdocument,applilcation/x-ms-xbap,"
               +"application/vnd.ms-powerpoint,application/msword,*/*");
        conn.setRequestProperty("Accept-Language","zh-CN");
        conn.setRequestProperty("Charset","UTF-8");
        conn.setRequestProperty("Connectoin","Keep-Alive");
        //得到文件大小
        fileSize = conn.getContentLength();
        conn.disconnect();
        int currentPartSize = fileSize / threadNum+1;
        RandomAccessFile file = new RandomAccessFile(targetFile,"rw");
        //设置本地文件大小
        file.setLength(fileSize);
        file.close();
        for (int i=0;i<threadNum;i++){
            //计算每个线程下载的开始位置
            int startPos = i * currentPartSize;
            //每个线程使用一个RandomAccessFile进行下载
            RandomAccessFile currentPart = new RandomAccessFile(targetFile,"rw");
            //定位该线程的下载位置
            currentPart.seek(startPos);
            //创建下载线程
            threads[i] = new DownThread(startPos,currentPartSize,currentPart);
            //启动下载线程
            threads[i].start();
        }
    }


    //获取下载的完成百分比
    public double getCompleteRate(){
        //统计多个线程已经下载的总大小
        int sumSize = 0;
        for (int i=0; i<threadNum; i++){
            sumSize += threads[i].length;
        }
        //返回已经完成的百分比
        return sumSize * 1.0/fileSize;
    }

    public class DownThread extends  Thread {
        //当前线程的下载位置
        private int startPos;

        //定义当前线程负责下载的文件大小
        private int currentPartSize;

        //当前线程需要下载的文件块
        private RandomAccessFile currentPart;

        //定义该线程已下载的字节数
        public int length;

        public DownThread(int startPos,int currentPartSize,RandomAccessFile currentPart){
            this.startPos = startPos;
            this.currentPartSize = currentPartSize;
            this.currentPart = currentPart;
        }

        public void run(){
            try {
                URL url = new URL(path);
                HttpURLConnection conn = (HttpURLConnection)url.openConnection();
                conn.setConnectTimeout(5*1000);
                conn.setRequestMethod("GET");
                conn.setRequestProperty("Accept","image/gif,image/jpeg,image/pjpeg,image/pjpeg," +
                        "application/x-shockwave-flash,application/xaml+xml"
                        +"application/vnd.ms-xpsdocument,applilcation/x-ms-xbap,"
                        +"application/vnd.ms-powerpoint,application/msword,*/*");
                conn.setRequestProperty("Accept-Language","zh-CN");
                conn.setRequestProperty("Charset","UTF-8");
                InputStream inStream = conn.getInputStream();
                //跳过startPos个字节，表明该线程只下载字节负责的那部分文件
                inStream.skip(this.startPos);
                byte[] buffer = new byte[1024];
                int hasRead=0;
                //读取网络数据，并写入本地文件
                while (length < currentPartSize && (hasRead = inStream.read(buffer))!= -1){
                    currentPart.write(buffer,0,hasRead);
                    //累计该线程下载的总大小
                    length += hasRead;
                }
                currentPart.close();
                inStream.close();

            } catch (MalformedURLException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }

    }
}
